Method of conditioning boiler water



Patented Jan. 1, 1946 UNITED STATES METHOD OF 2,391,895 ONDITIONINGBOILER WATER Lewis 0. Gunderson, Park Ridge, Iil., assignor to DearbornChemical Company, Chicago, 111., a

corporation of Illinoi No Drawing. Application March 18, 1942, SerialNo. 435,223

19 Claims.

This invention relates to a method of conditioning boiler water for theprevention or reduction of foaming in boilers, for the prevention orreduction of moisture entrainment in steam produced from effervescentwaters, for the prevention or reduction of siliceous scale formation inboilers, for the prevention or reduction of intercrystalline cracking ofthe boiler steel, for the prevention or reduction of corrosion of boilermetals, and for the solubilization of calcium and magnesium sludges inboiler water.

This application is a continuation-in-part of my pending applicationSerial No. 261,683, entitled "Method of conditioning boiler water, filedMarch 13, 1939.

One of the major problems confronting all industries concerned with thegeneration of steam, whether it be for railroad locomotives, stationarypower plants, or marine boilers, is the serious damage to reciprocatingengines, turbines or other prime movers due to the carry over of waterwith the steam. Such carry over results in deposits of mineral matter insuperheaters, throttles, valves, cylinders, turbine blades and the like.

This water carry over is the result of phenomena known'as boiler foamingand as effervescence. Boiler foaming occurs when the steam bubblesenerated within the boiler show increased resistance to coalescenceresulting in gradually increased expansion of the boiler water in thesteam generating area with more or less accumulation of foam at thesurface, until finally the entire steam space is closed oil. and foam isentrained with the steam leaving the boiler.

The term effervescence signifies the phe-- nomenon of steam bubblesrising through the water and bursting at the surface with consider.-able violence causing the projection of water droplets for considerabledistances above the water surface. The smaller of such droplets areentrained with the steam leaving the boiler. The entrainment of moistureresulting from this effervescence is proportional to the rate of steamdraw off. When the velocity of the steam above the water surface is verygreat, the entrainment "of water particles projected into the steamspace'by effervescence is particularly great. It is obvious that watercarry over due to effervescence will be the greater the closer the watersurface is to the steam outlet. Therefore, if a boiler water hasconsiderable foaming tendency, coupled with an effervescent character,water entrainment by the steam will occur, first, by the carry over ofparticles of moisture projected into the steam spaceby effervescence,and, periodically, by the carry over of the foamy surface layer of thewater itself, involving a much larger percentage of boiler waterentrainment with the steam.

Although there are numerous factors affectin foam formation, it appearsthat the function of surface-active organic matter is of primaryimportance in the formation of foam. Potentially surface-active organicmatter contained in boiler feed waters obtained from surface supplies aswell as from deep wells, tends to be adsorbed by colloidal materialdispersed in the boiler water, par.-

ticularly at certain concentrations of dissolved and dispersed matter.The exact concentrations at which such adsorption will occur depends onthe prevailing alkalinity, the nature of the adsorbed organic materialand on the nature of the dissolved mineral matter encountered in feedwater from various sources. Such adsorption results in the mutualincrease of surface-activity of the organic matter and the dispersedmatter causing adsorption in the steam bubble films and w ter surfac sto theextent of forming more or less stable surface films. Foaming isthought to be due to the formation of such stable surface films.

I have found that there is a correlation between surface tension andwater carry over due to ffervescence. The higher the surface tension,the greater will be the tendency toward carry-over due to eifervescence.It is believed that relatively higher surface tension is accompanied byincreased hydration of the surface films in the boiler water. On theother hand, the foaming tendency of the boiler water is not necessarilycorrelated with the magnitude of the surface tension of the water,although it has been observed that maximum development of foam generallyis associated with a considerable decrease in surface tension. Foamformation may occur when relatively high surface tension prevails. Undersuch circumstances foam formation may involve a rather large carry overof water, since the amount of water contained within the surface filmsmay be large.

The present invention provides a method that will eliminate theformation of foam and will prevent the undesirable expansion oftheboiler water in the steam generating zone, thus maintaining thesurface of the water in the boiler at a low level. Under such conditionsa maximum steam space and minimum steam velocity are maintained. Anywater droplets projected into the steam space by the rupture of steambubbles will be pulled back to the water surface by gravity before thedroplets can reach the steam outlet.

I believe that'the m ethod of this invention brings about the aboveindicated effects by eliminating the forces tending to prevent thecoalescence of steam bubbles and by providing surface filmscharacterized by a surface tension and a surface film hydration that donot reach undesirably high values.

My process compri incorporatin with the boiler water colloidal micellescontaining silica and heavy metal oxides or hydroxides wherein the ratioof silica to metal oxide is relatively large, preferably at least 4to 1. Such micelles are believed to prevent foam formation due to theiraction on the potentially surface-active organic matter contained inboiler feed waters and boiler waters.

Besides preventing or lessening foam formation and water entrainment,the provision of such micelles in boiler water will prevent or reducesiliceous scale formation in boilers, intercrystalline cracking ofboiler steel, corrosion of boiler metals and will solubilize .calciumand magnesium sludges in boiler waters.

It is therefore an important object of the present invention to providemethods of conditioning boiler water and boiler feed water that willgenerally facilitate the operation of steam boilers and preventdeterioration of steam boilers.

Another object ofthe present invention is to provide a method oftreating boile water and boiler feed water that will accomplish thespecific advantages mentioned hereinabove.

A further object of this invention is to provide a method of treatingboiler water and boiler feed water by incorporating therein siliceousmicelles containing heavy metal oxides, the silica-metal oxide ratiopreferably being at least 4 to 1.

Another and further objects and features of this invention will becomeapparent from the following detailed description and appended claims.

In Order to provide colloidal micelles of the nature indicated, I preferto add to boiler water or boiler feed water colloidal silicic acid.Soluble heavy metal salts are also added that will, onbeing added toconventionally softened and hence alkaline boiler feed waters, producethe corre-' sponding metal oxide or hydroxide. Such metal oxides andhydroxides have high afllnitie for colloidal silica. By adding traces Orvery small amounts of the metal salts, the desired high silica-metaloxide ratio is assured. I believe that the efiect of these additions canbe explained by the resulting formation of micelles which adsorb largequantities of organic matter from the boiler feed water or the boilerwater and thus prevent this organic matter from forming and stabilizingfoam. However, knowledge of the complete mechanism of the reactionwhereby the desired results are obtained is not necessary for carryingout the method of this invention for the purpose indicated.

The desired silica-metal oxide hydrosols having a high silica-metaloxide ratio may thus be produced by the separate but optionallycontemporaneous addition of colloidal silicic acid and heavy oxides toboiler water or boiler feed water. The same hydrosols may be produced bymixing colloidal silicic acid with dilute solutions of heavy metalcompounds in a separate container. These two substances after beingmixed are diluted greatly to form a 2 to solution of silica-heavy metaloxide hydrosols, which dilute solution can then be added to the boilerfeed water at a ratio such that the boiler feed water will be treatedwith approximately 0.02 to 5 parts per million of heavy metal compoundsand from 0.08 to 0.120 or more parts per million of colloidal silicicacid. This rate of addition is also that preferred when the siliceousand metalliferous ingredients are added separately. The above mentioneddilute solution of inorganic micelles may also contain cooperativereagents mentioned elsewhere in this application, such as carboxyllcacids and their alkali salts, sodium nitrate, organic protectivecolloids such as tannins, lignin, and the like.

The method of this invention is particularly designed for treatingconventionally softened boiler feed waters such as are almostuniversally used in this country. Conventional softening usually takesthe form of addition of soda ash or caustic soda directly to the boilerfeed waters before delivery of the latter to the boiler. Sometimes thesoda ash or caustic soda are compounded with various organic materials,a in many proprietary boiler water treatments, or soda ash inconjunction with lime may be used in a lime-soda softener wherein thecalcium and magnesium sulfates and bicarbonates are precipitated almostcompletely before the water is delivered to the boiler. The method ofthis invention is also suitable for use with zeolite softened water. Inany case, the boiler feed waters conventionally are provided with excesssodium alkalinity equivalent to 15 to 30% of the total dissolved solids.Initiation of the present process, particularly in locomotive boiler, isbest carried out with an excess alkalinity of at least 30% of thedissolved solids in the boiler water. Subsequently, as the concentrationof dissolved 501- I ids in the boiler water increases, it is possible todecrease the alkalinity to 10% of the total solids or less, thuseffecting a saving in the amount of softening chemicals required for theboiler feed waters.

Any f the soluble salts (such as the sulfates,

' chlorides, and nitrates) of the heavy metals,

which for the purpose of this invention may be defined as any metalhaving a density greater than 4, for instance, manganese, chromium,cobalt, zinc, zirconium, thorium, tin, nickel, titanium, vanadium, andothers, are operative when used to form the metal oxide ingredient ofthe inorganic micelles thought to be the eillcient factors in foamprevention according to my method. Any one of the heavy metal salts maybe used or any combination of heavy metal salts. The salts may be addedin aqueous solutions or in powdered crystalline form to boiler water orboiler feed water. Colloidally dispersed metal oxides or hydroxides mayalso be added.

Only very small amounts or traces of heavy metals need be added to brinabout the desired results. A preferred dosage is from about 0.02 to 0.05parts per million of boiler water. In the case of. greatly contaminatedboiler feed oxide hydrosols. These boiler feed waters are water orboiler water, the amount of heavy metal salt, oxide or hydroxide may beincreased, the amount of silicic acid added being increasedcorrespondingly. Generally not more than two parts per million of heavymetal oxide are added, the upper limit being not more than five partsper million.

Precau'ticn should be taken, when the heavy metal compounds are added toboiler feed water, to guard against removal by flocculation orabsorption of the heavy metal oxides or hydroxides produced by addingheavy metal salts to alkaline boiler feed water. Protective colloid suchas tannin, suliite waste liquor, gum arabic or the like may be added tothe feed water. Peptizing agents may also be added, for instance, alkalinitrates, alkali sulfocyanides, alkali thiocyanates, thiourea and thelike. Tan in or like protective colloids may be added at a rate of about6 to 12 parts per million. Sodium nitrate fed at the rate of at least 20arts per million may be substituted for the tannin.

As an illustration of the manner of adding heavy metal compounds may bementioned the use of a solution containing manganese sulfate and 5%chrome alum (chromium potassium sulfate). By means of a suitableproportioning mechanism this solution maybe automatically fed to boilerfeed water flowing into a locomotive water tender at the rate of 0.02parts of heavy metal compound per one million parts of water.

In some territories boiler feed waters may be obtained that naturallycontain enough colloidal silica for combination with heavy metalcompounds added as disclosed hereinabove to prevent foam formation,However, to insure proper foam prevention, it is desirable to add, inall cases, colloidal silicic acid in amounts suflicient to establish thedesired silica-heavy metal oxide ratio. An excess of silica, is notharmful. The colloidal silicic acid is preferably added as a diluteacidified solution, which on aging becomes more efficient for foamprevention. This improved foam prevention is thought to be due topolymerization of the silicic acid molecules on standing of theacidified colloidal solution.

In the case of locomotive boilers, such aged or polymerized silicic acidsolution may be fed to boiler water flowing into a locomotive tender bysuitable proportioning means to treat such water at the rate of 0.120parts of silica per one million parts of water. Preferably this silicicacid is fed into the boiler water at the same time as the heavy metalcompounds are added to the water and in such a manner that the silicaand heavy metal compounds will commingle as much as possible. The ratioof silica to metal oxide should be at least 4 to 1 and preferably atleast 6 to 1. When boiler feed water is treated that is known to containconsiderable amounts of colloidal silicic acid, the amount of the addedcolloidal silicic acid may be reduced accordingly.

In some territories boiler feed waters contain large quantities ofalkali salts, for instance, in excess Of 500 parts per million of alkalisulfates or chlorides, together with greater or smaller amounts ofcalcium and magnesium compounds. Such waters usually contain relativelylarge amounts of dissolved silica. When the silica content isconsiderable, such as 4% or more of the total dissolved solids, itappears that an appreciable portion of this silica is present in theform of colloidal silicic acid or hydrated silica-metal usually amenableto processing by the addition of suitable heavymetal compounds alone.This is particularly true where these waters contain considerableamounts of sodium bicarbonate or free carbon dioxide dissolved in theboiler water, for the carbonic acid tends to force silica into thecolloidal state.

A possible explanation for the foam prevention effected according tothis invention by the addition of heavy metal compounds and enoughcolloidal silica to make up a heavy metal oxidesilica ratio of at least1 to 4 is the above-mentioned formation of micelles due to theadsorption of the heavy metal oxides or hydroxides by the colloidalsilicic acid. As surface-active foam forming and foam stabilizingorganic matter is progressively adsorbed by the highly siliceousmicelles the latter will become increasingly more surface-active andwill accordingly be adsorbed in the steam bubble films and the watersurfaces.

There will thus be formed concentrated surface layers or adsorptivesiliceous micelles which will continue to adsorb surface-active organicsubstances that naturally accumulate in the steam bubble films and thewater surfaces. Such progressive adsorption of organic substances willeventually cause flocculation of the inorganic micelles together withtheir loads of adsorbed organic matter. The flocculated micelles willaccordingly be precipitated to the bottom of the boiler where theprecipitate can be removed by blowing off through the blow-off valve.

The present invention involving the addition of heavy metal compoundsand of enough colloidal silicic acid Lo effect a metal oxide-colloidalsilica ratio of at least 1 to 4 should be clearly distinguished fromconventional addition of metal compounds such as alum or aluminumsulfate for the purpose of clarifying or otherwise purifying water. Suchconventional treatment involves the addition of metal compounds far inexcess of the amounts added according to the present invention, whichgenerally do not exceed five parts per million and as a rule are lessthan two parts per million.

The present method should also be distinuished from conventional methodsof addin heavy metal salts to water containing dissolved silica for thepurpose of removing the dissolved silica. In the conventional treatment,the heavy metal salts are added in at least stoichiometrical proportionsto the total silica present, whereas in the present invention heavymetal compounds are added in less. than stoichiometrical proportions tothat part of the silica present in colloidally dispersed form.

I have found it advantageous to add the heavy metal compounds suspendedin vehicles including a sodium hydroxide solution having organicprotective colloids incorporated therewith, for instance, quebrachoextract, tannin and the like. Such preparations, besides beingnon-freezing and non-corrosive, have some softening effect when added tothe boiler feed water. The heavy metal compounds contained in suchpreparations are thought to be in a colloidally dispersed state. It isbelieved that when such preparations are fed to boiler feed water at therate, say, of 0.02

parts per million of the metal compound, the

resulting dilution will cause formation of the corresponding metal oxideor hydroxide which will subsequently react with appropriate amounts ofcolloidal silica to form the desired inorganic hydrosol. A formula forpreparing a ten-drum batch of such a preparation is given hereinbelow byway of an example.

Percent Pounds Water 32. 5 l, 950 Chromium suliate 3. 0 Manganoussulfata l. 0 60 Tartaric acid 4. 0 240 Cane sugar 4. 0 240 Stannicchloride (cont mg 5 molecules of water of crystallization) 0. 3 18 Zincchloride (anhydrous) 0.2 12 Liquid caustic soda 40. 0 2, 400 Liquidquebracho 15. o 900 The preparation may be made up by running sulfateand 40 pounds of tartaric acid are added and stirred until dissolved.Then 18 pounds of stannic chloride and 12 pounds of zinc chloride areadded and stirring is continued until all the material is in solution.The mixture is then weighed and the amount of condensate from the steamused for heatingand agitation is determined. About four gallons ofcondensate are usually formed in this operation.

Then the balance of the water specified in the formula, or approximately1700 pounds (2100 pounds less.250 pounds condensate to be expected) arerun into a mixing tank equipped with a mechanical stirring device. 200pounds of tartaric acid and 240 pounds of cane sugar are added whilecontinuous agitation is effected. The chromium sulfate, manganesesulfate, tartaric acid, stannic chloride and zinc chloride solutionwhose preparation has been described in the preceding paragraph is thenadded. Then, with constant agitation,-2400 pounds of liquid caustic sodaand finally 900 pounds of liquid quebracho extract are run in. Thepraparation is then mixedthoroughly for about fifteen minutes before itis run into steel drums for shipment.

The same composition may b prepared with stannous chloride substitutedfor stannic chloride, which is difficult to store and handle. An amountof stannous chloride containing as much tin as the specified amount ofstannic chloride is dissolved in 100 pounds of water. 6 pounds oftartaric acid are added and stirred into solution. No heat is requiredto dissolve either the stannous chlorid or the tartaric acid. An amountof sodium dichromate appropriate to convert the stannous chloride tostannic chloride is then added, followed by 60 pounds of liquid causticsoda. After reaction the completed mixture is ready for incorporation inthe regular formula as originally described. The amount of chromiumobtained from the sodium dichromate is calculated to chromium sulfateand subtracted from the total amount of chromium sulfate required in thecomplete formula. The reaction between the stannous chloride, sodiumdichromate and sodium hydroxide is very violent. A large amount of heatis evolved and for better control of the reaction no heat should beapplied at any stage of this reaction.

Chrome alum may be used in place of chromium sulfate, the specifiedpercentages of all the constituents being retained. The reduced chromiumcontent of the resulting preparation does not affect the action of theformula.

The liquid caustic content of the formula may be reduced to 30% and theliquid quebracho extract may be increased to 40%, with a correspondingmodification of the water content, to make a stable preparation.

In the above preparation the chromium, thought to be present in the formof colloidal chromium hydroxide, is effective to keep the other metaloxides in colloidal solution. The tartaric acid and the sugar arestabilizing agents preventing precipitation of the colloidally dispersedmatter, the tartaric acid being particularly effective to solubilize thechromium hydroxide. The tartaric acid may be reduced to 1% withoutjeopardizing the stability of the preparation. In place of tartaric acidalkali tartrates or Rochelle salts may be used.

Changes other than those indicated may also be made in the aboveformula, which is given solely by way of an illustrative example.

Powdered preparations may also be applied to furnish boiler water withheavy metal compounds as called for by the method of this invention.Examples of formulae for such compositions are given hereinbelow.

These two formulae yield compositions designed for addition to boilerfeed water at the rate of one pound for each 10,000 gallons and may beadded directly to the locomotive boiler water tender when taking waterso as to insure good mixing of the chemicals withthe water. Formula A isdesigned for boiler feed waters that have relatively low excessalkalinity either as sodium carbonate or as caustic soda. Formula 13would serve for addition to boiler feed waters that have relativelyhigher excess sodium alkalinity either as sodium carbonate or causticsoda, such as 6 to 10 grains of alkalinity expressed as sodiumcarbonate. The purpose of the sodium carbonate in Formula A is to insurean alkaline medium for the heavy salts capable of converting the heavymetal salts to their oxides or hydroxides. These formulae for powderedcompositions are only given as examples of preparations of this type.Many other formulae can be made up that yield compositions that willfunction in a similar manner.

An example of a preparation of colloidal silicic acid will now be given.

Procedure 4359 pounds (524 gallons) of water are run into a mixing tankequipped with a mechanical stirring device or air agitator. 188.1 lbs.of a sodium silicate solution having a density of 35.5 Baum andcontaining 6.3% NazO together with 24.6% S10: are added and mixedthoroughly. 45.0 pounds of the dilute sulfuric acid are then added withconstant stirring. The alkalinity of the resulting mixture is determinedin a 50 cc. sample by titration to a methylorange end point with N/ 10sulfuric acid. 'A titration value of 12 to 13 cc. of N/ 10 sulfuric acidon a 50 cc. sample is desired. This titration value is equivalent to analkalinity of 1200 to 1300 parts per million. Additional dilute sulfuricacid is added until the desired titration is obtained. The 50.6 poundsof dilute sulfuric acid specified in the formula is only an average orapproximate value. Each batch prepared requires somewhat differentamounts of acid. Addition of excess acid and restoration to properalkalinity should be avoided.

When the alkalinity has been properly ad- Justed, 2.3 pounds of liquidquebracho extract are added, and the material is thoroughly mixed andrun into containers coated on the inside with high melting petrolatum.Uncoated drums have been found to promote local gel formation at theliquid surface contracting the drum.

This colloidal silicic acid solution, when properly prepared, is quitestable and will retain its colloidal nature for a satisfactory period oftime.

Any other sodium silicate than the particular solution disclosedhereinabove may be used in preparing colloidal silicic acid according tothe above formula, although the disclosed solution is more satisfactorydue to its relativel high silica content. This allows the use of asmaller amount of acid in the reduction of the alkalinity and aconsequent smaller total solids content in the finished composition,which has been found to promote stability. When any other sodiumsilicate is used, the amount used should be adjusted to provide a 1%silica (S102) content in the finished composition.

Compositions such as those disclosed hav been successfully used tocondition water to a permanently non-foaming condition in a modernlocomotive boiler operating over 700 miles of track for 18,000 milesthrough a recognized bad water territory where foaming is a, commonoccurrence. The average concentration of boiler water ,salinesmaintained normally without my treatment approximates 3000 parts permillion, requiring a blow-down waste of approximately of the feed waterused, whereas after my conditioning process becomes fuly effective, a.saline concentration of over 59,000 parts per million was reachedwithout requiring any blowdown. This performance has been duplicated onrailroads in widely separated parts of this country, producingnon-foaming boiler waters having saline concentrations reaching over35,000 parts per million.

It has been found from actual experience in railroad service that it isnot absolutely essential to add the conditioning composition orcompositions every time boiler feed water is added to the locomotivetender. The conditioning compositions may be added only at some of theboiler feed supplies, for instance, at every other water station wherea, locomotive is supplied with feed water. The functioning of the foampreventing process appears to become progressively effective the longerthe boiler is in use, lesser and lesser amounts of conditioningcomposition being required.

The above disclosed method of conditioning is effective not only toprevent or reduce water carry over due to foaming or efiervescence butalso has a remarkable effect on precipitated calcium and magnesiumsludges in boiler water.

Such sludges are preventing from precipitating.

bilized or dispersed in the boiler water. A possible explanation forthis fact is that the siliceous micelles may peptize the calcium andmagnesium carbonates to the extent that the same are colloidally orotherwise dispersed. Possibly the micelles, being highly hydrated, serveto render the sludge sufiiciently hydrated to prevent accumulation ofthe sludge particles as a packed dense mass at the bottom of the boiler.This prevention of caking is an important feature of the present method,which lessens the amount of blowing off required to an extent thatotherwise would permit the accumulation of undesirable crystallinesludges in the bottom portions of the boiler. Thus the lessenedblowing-off obtained by the present method is not accompanied by anydanger of crystalline deposits forming in the boiler, so that thebenefits accruing from the. practical elimination of blow-offs can befreely made use of.

In the case Of feed waters that naturally contain large amounts ofsilica, the addition of tartaric or citric or oxalic acids or othercarboxylic acids or alkali salts thereof improves the functioning of mymethod of preventing foam formation. The same is true of inorganic saltssuch as nitrates, chlorides or sulfates, although much largerconcentrates of such inorganic salts are required for the same results.-I prefer to use Rochelle salts, tartaric acid, or the alkali tartrates,added to the boiler feed water at the rate of approximately 0.1 part permillion or more, depending on the specific character of the boiler feedwaters encountered. The mechanism by which these salts and acidscontribute to the prevention of the foam formation is not certain.However, it is presumed that the anions of these salts or acids areadsorbed by the inorganic micelles, displacing adsorbed water and thusdehydrating the micelles. Much greater concentrations of alkali sulfatesor ch10- rides or the like have the same effect. The addition of smallconcentrations, say, not more than one part per million, of carboxylicacid or alkali carboxylates is therefore particularly useful in theinitial stages of the processing of water in districts where the boilerfeed waters have a, relativel low alkali salt content, 1. e., less than400 parts per million. At the initiation of treatment according to thepresent method, after washout or water change in the boiler, sodiumcarbonate, sodium sulfate or other alkali salts may be added at the rateof 400 parts per million or more, in place of or together withcarboxylic acids or salts.

The usual railroad practice is to wash out locomotive boilers at leastonce a month in compliance with Federal "statutes. Very often theboilers are given water changes or boiler washouts at more frequentintervals, at which time the concentrated boiler water is blown off intoa storage tank or reservoir, or is run off to waste. If saved, thisboiler water is customarily used for washing out other boilers andsubsequently run off to waste. conditioned by my method permits steamgeneration without carry over of Water and contains, besides a desirableconcentration of softening chemicals such as sodium carbonate andcaustic soda, alkali salts such as sulfates and chlorides built up to aconcentration such that very little and in some cases no additionaladdition of colloidal silica and heavy metal compounds are required tomaintain a non-foaming Boiler water that has been condition. For thisreason, it is advisable to collect and reuse boiler water conditionedaccording to my process rather than to start conditioning with untreatedwater and by addition of conditioning agents and gr .dual increase inconcentration of dissolved solids gradually reach a permanently oralmost permanently non-foaming and non-eifervescing condition, as may bedone b the present conditioning method. The boiler water content ofsodium carbonate usually is converted to sodium hydroxide after longperiods in the boiler. The carbonate ion is usually thought moredesirable in boiler water than the hydroxide ion. Therefore, waste fluegases or other gases containing carbon dioxide may be passed through theused boiler water before reuse.

The maintenance of silica-metal oxide hydrosols in boiler water, ascalled for by the present invention, will also prevent the so-called"intercrystalline cracking of the boiler metal along leaky seams,especially in the presence of the supplementary substances used in myprocess, such as the carboxylic acids and their salts, alkali nitrates,tannins and the like. This preventive action I believe to be due to theflocculation or precipitation of the micelles in or on the metal grainboundaries to insulate these areas from the caustic boiler water,Apparentl the micelles adsorb the metal ions set free at metal surfacesbeing corroded so that the micelles have their silica-metal oxide ratioprogressively reduced to the point where the micelles are precipitatedas metal silicates on or adjacent the metal surface being corroded,whereby the latter is sealed off from contact with the corrodingsolution. At least the precipitated micelles will prevent the exit ofdissolved metal ions from boiler water confined within cracks in theboiler metal, so that this confined water will soon become saturatedwith metal ions and hence be unable to effect further corrosion.

Oxidizing agents, in particular, sodium nitrate, make for more eflicientprevention of intercrystalline cracking. This eifect is probably due toan oxidation of the metal surface being corroded to theferric state,converting this surface to ferric oxide or hydroxide which is stronglyadsorbed by the siliceous micelles. Therefore, any suitable oxidizingagent used in conjunction with the siliceous micelles will aid inpreventing grain boundary corrosion and crystalline embrittlement. Themetal may also be preoxidized with a strong oxidizing agent before wateris admitted into the boiler. The oxidized surface may then reactmetathetically with the'siliceous micelles to form a protective layer,

General corrosion of the bo ler metal is prevented similarly to theprevention of intercrystalline cracking by the metal oxide-silicahydrosols used in the present invention, particularly when used inconjunction with sodium nitrate or other oxidzing agents, as describedhereinabove.

Operation in a boiler of my foam prevention process also eifects theremoval of siliceous scale as well as the inhibition of formation of newsiliceous scale. This result is believed due to the higher causticalkalinity and total solids concentration that can be maintained inboiler water treated according to my process, which would promotedissolution of the silica.

Many details of composition and procedure may be varied withoutdeparting from the principles of tlis invention and without sacrificingthe advantages mentioned hereinabove. It is therefore not my purpose tolimit the patent granted on this invention otherwise than necessitatedby the scope of the appended claims.

What I claim is:

1. The method of conditioning water for steam generation, whichcomprises incorporating with said water from a trace to flve parts permillion of a heavy metal compound selected from the group consisting ofthe colloidal oxides, the colloidal hydroxides, and the water solublesalts capable of forming colloidal oxides and hydroxides in said water,and incorporating with said waterii'ifllcient colloidal silica toestablish in said water a colloidal silica-heavy metal oxide ratio of atleast four to one.

2. The method of conditioning water for steam generation which comprisesincorporating with said water from a trace to two parts per million of aheavy metal compound selected from the group consisting of the colloidaloxides, the colloidal hydroxides, and the water soluble salts capable offorming colloidal oxides and hydroxides in said water, and incorporatingwith said water suillcient colloidal silica to establish in said water acolloidal silica-heavy metal oxide ratio of at least four to one.

3. The method of conditioning water for steam generation which comprisesincorporating with said water from a trace to five parts per million ofa heavy ,metal compound selected from the group consisting of thecolloidal oxides, the colloidal hydroxides, and the water soluble saltscapable of forming colloidal oxides and hydroxides in said water, andincorporating with said water sufllcient colloidal silica to establishin said water a colloidal silica-heavy metal oxide ratio of at least sixto one.

4. The method of conditioning water for steam generation which comprisesincorporating with said water from a trace to two parts per million of aheavy metal compound selected from the group consisting of the colloidaloxides, the colloidal hydroxides and the water soluble salts capable offorming colloidal oxides and hydroxides in said water, and incorporatingwith said Water sufllcient colloidal silica to establish in said water acolloidal silica-heavy metal oxide ratio of at least six to one.

5. The method of conditioning boiler water for steam generation whichincludes incorporating with said water from a trace to five parts permillion of a water soluble heavy metal compound capable of forming acolloidal oxide and hydroxide in said water and incorporating with saidwater sufllcient colloidal silica to establish in said water a colloidalsilica-heavy metal oxide ratio of at least four to one.

6. The method of conditioning boiler water for steam generation whichincludes incorporating with said water from a trace to five parts permillion of a water soluble heavy metal salt capable of forming acolloidal oxide and hydroxide in said water and incorporating with saidwater sumcient colloidal silica to form in said water a heavy metaloxide-silica lrydrosol having a silica-heavy metal oxide ratio of atleast four to one.

'7. The method of conditioning alkaline boiler water which includesincorporating with said water a water soluble heav metal ,salt inamounts varying from a trace to five parts per million, incorporatingwith said water at least 0.120 parts per million of colloidal silica toform a silica-heavy metal oxide hydrosol having a silica-heavy metaloxide ratio of at least 4 to 1,

and incorporating with said water a compound capable of formingcarboxylic anions in said water when dissolved therein.

8. The method of conditioning alkaline boiler water which includesincorporating with said water a water soluble heavy metal salt inamounts varying from a trace to five parts per million, incorporatingwith said water at least 0.120 parts per million of colloidal silica toform a silica-heavy metal oxide hydrosol having a silica-heavy metaloxide ratio of at least 4 to 1. and incorporating with said water atleast 20 parts per million of sodium nitrate.

9. The method of conditioning alkaline boiler water for steam generationwhich includes incorporating with said water from a trace to five partsper million of a water soluble heavy metal salt capable of forming acolloidal oxide and bydroxide in said water, incorporating with saidwater a quantity of colloidal silica amounting at least to 0.120 partsper million and sufilcient to form in said water a silica-heavy metaloxide hydrosol having a silica-heavy metal oxide-ratio of at least fourto one, and incorporating a protective colloid with said water toprevent precipitation of heavy metal oxides.

10. The method of conditioning alkaline boiler water for steamgeneration, which includes incorporating with said water from a trace tofive parts per million of a water soluble heav metal salt capable offorming a colloidal oxide and hydroxide in said water, incorporatingwith said water a quantity of colloidal silica amountin at least to0.120 parts per million and sufflcient to form a silica-heavy metaloxide hydrosol having a silica-heavy metal oxide ratio of at least fourto one, and incorporating with said water a peptizing agent to preventprecipitation of heavy metal oxides.

11. The method of conditioning boiler water for steam generation whichincludes establishing a total solids content of at least four hundredparts per million and a sodium alkalinity of at least 15 parts permillion in said water, incorporating with said water from a trace tofive parts per million of a heavy metal compound selected from the groupconsisting of the colloidal oxides, the colloidal hydroxides, and thewater soluble salts capable of forming colloidal oxides and hydroxidesin said water, and incorporating with said water suillcient colloidalsilica to establish in said water a colloidal silica-heavy metal oxideratio of at least four to one.

12. The method of preventing intercrystalline cracking and corrosion ina boiler, which includes incorporating with the boiler water from atrace to five parts per million of a heavy metal compound selected fromthe colloidal oxides, the colloidal hydroxides, and the water solublesalts capable of forming colloidal oxides and hydroxides in said water.and incorporating with said water sufficient colloidal silica toestablish in said water a colloidal silica-heavy metal oxide ratio of atleast four to one.

18. The method of conditioning boiler water containing at least 0.120parts per million of colloidal silica which includes incorporating withsaid water a water soluble heavy metal salt in an amount ranging from atrace to five parts per million and adapted to form a silica-heavy metaloxide hydrosol having a silica-heavy metal oxide ratio of at least 4 to1.

14. The method of conditioning boiler water which includes incorporatingtherewith a colloidal heavy metal oxide in amounts varying from a traceto five parts per million and incorporating with said water sumcientcolloidal silica to establish in said water a colloidal silica-heavymetal oxide ratio of at least 4 to l.

15. The method of conditioning boiler water which includes incorporatingwith said water colloidal chromium hydroxide in amounts varying from atrace to five parts per million and incorporating with said watersufflcient colloidal silica to establish in said water a colloidalsilica-heavy metal oxide ratio of at least 4 to l.

16. The method 01' conditioning boiler water which includesincorporating with said water colloidal chromium hydroxide dispersed ina sodium hydroxide solution together with other heavy metal oxides alsodispersed in said sodium hydroxide solution, the total amount 01' heavymetal oxides and hydroxides in said water after said incorporationvarying from a trace to five parts per million, and incorporating withsaid water sufllcient colloidal silica to establish. in said water acolloidal silica-heavy metal oxide ratio of at least 4 to 1.

17. A composition for treating boiler water comprising an aqueous 2 to5% colloidal solution containing colloidal silicic acid and a heav metaloxide in a ratio of at least 4 to l.

18. The method of preventing intercrystalline cracking and corrosion ina boiler which includes incorporating with the boiler water an oxidizingagent capable of oxidizing the boiler metal surface, incorporating withthe boiler water from a trace to five parts per million of a heavy metalcompound selected from the colloidal oxides, the colloidal hydroxides,and the water soluble salts capable of forming colloidal oxides andhydroxides in said water, and incorporating with said water suificientcolloidal silica to establish in said water a colloidal silica-heavymetal oxide ratio of at least six to one.

19. The method of preventing intercrystalline cracking and corrosion ina boiler, which includes preoxidizing the boiler metal surface,incorporating with the boiler water from a trace to five parts permillion of a heavy metal compound selected from the group consisting ofthe colloidal oxides, the colloidal hydroxides and the water solublesalts capable of forming colloidal oxides and hydroxides in said water,and incorporating with said water sufficient colloidal silica toestablish in said Water a colloidal silica-heavy metal oxide ratio of atleast four to one.

LEWIS O, GUN'DERSON.

